This invention pertains to coextruded plastic films, and particularly, to those films having a polypropylene layer adhered to a layer of a nylon-type polyamide. In such films, the adhesion between the nylon and polypropylene layers has been particularly troublesome. It has been surprisingly found that an excellent adhesive for the coextrusion of nylon and polypropylene is a blend of a graft copolymer of maleic anhydride onto an olefin polymer or copolymer and an ungrafted propylene-based polymer. The graft copolymer typically contains from about 0.10% to about 2.5% maleic anhydride based on the total weight of the graft copolymer, and must contain from about 0.005% to 0.75% maleic anhydride based on the total weight of the entire blend composition.
In the coextrusion of a 5-layer film, the structure may include a fourth layer, of ethylene vinyl alcohol copolymer (EVOH), affixed on one of its surfaces to the nylon, and a fifth layer, of nylon, affixed to the other surface of the EVOH.
Thus the process comprises coextruding polypropylene, and nylon with the adhesive blend juxtaposed therebetween. In the formation of a five layer structure containing EVOH, the process comprises coextruding the five layer structure of, in sequential order in the structural layering, from one outside surface to the other: polypropylene, adhesive blend, nylon, EVOH, and nylon.